Water-Based Ink for Ink-Jet Recording and Ink Container

ABSTRACT

There is provided a water-based ink for ink-jet recording including: a self-dispersible pigment of which mean particle diameter is not less than 130 nm; a resin-dispersed pigment; and water; wherein the mean particle diameter of the self-dispersible pigment is in a range of 1.5 times to 3 times mean particle diameter of the resin-dispersed pigment.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. 2017-071135 filed on Mar. 31, 2017 the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND Field of the Invention

The present invention relates to a water-based ink for ink-jetrecording, and an ink container which accommodates the water-based inkfor ink-jet recording therein.

Description of the Related Art

For the purpose of obtaining a high optical density (OD value) in a caseof performing recording on plain paper (plain paper sheet), there isproposed a water-based ink for ink-jet recording (hereinafter referredto also as a “water-based ink” or an “ink” in some cases) using aself-dispersible pigment having a large mean particle diameter (see, forexample, Japanese Paten Application Laid-open No. 2004-203903).

In the above-described water-based ink using the self-dispersiblepigment having the large mean particle diameter, however, although ahigh optical density (OD value) can be obtained on the plain paper, theself-dispersible pigment generally has a low fixing property to glossypaper. On the other hand, a water-based ink using a resin-dispersedpigment has a high fixing property to the glossy paper, but has a lowoptical density (OD value) on the plain paper.

In view of the above-described situation, an object of the presentteaching is to provide a water-based ink for ink-jet recording which iscapable of realizing both the high optical density (OD value) in a caseof performing recording on the plain paper, and the high fixing propertyto the glossy paper.

SUMMARY

According to a first aspect of the present teaching, there is provided awater-based ink for ink-jet recording including:

water;

a resin-dispersed pigment; and

a self-dispersible pigment of which mean particle diameter is not lessthan 130 nm, and is in a range of 1.5 times to 3 times mean particlediameter of the resin-dispersed pigment.

According to a second aspect of the present teaching, there is providedan ink container which accommodates the water-based ink for ink-jetrecording of the first aspect therein.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a schematic perspective view depicting the configurationof an example of an ink-jet recording apparatus related to the presentteaching.

DESCRIPTION OF THE EMBODIMENTS

In the present teaching, the term “plain paper” means, for example,recording paper which includes high-quality paper used for a notebook, awriting pad, etc., copying paper having no coating applied thereto,etc., and which has no processing or coating processing performed on arecording surface thereof. The plain paper is exemplified, for example,by “Office Paper” manufactured by FUJITSU LIMITED; “Hammermill PaperLaser Print” manufactured by INTERNATIONAL PAPER COMPANY; “DATA COPYPAPER” manufactured by M-REAL CORPORATION; “Xerox 4200” manufactured byXEROX CORPORATION; “4200DP PAPER” manufactured by FUJI XEROX, LTD.; andthe like.

In the present teaching, the term “glossy paper” means recording paperhaving at least one layer of coating layer formed on a recording surfacethereof by using silica particles or alumina particles, etc. The glossypaper is exemplified, for example, by photo glossy paper BP61G, BP71Gand BP71GA4 manufactured by BROTHER KOGYO KABUSHIKI KAISHA; ink-jetpaper “KASSAI” photo finish gloss pro manufactured by FUJIFILMCORPORATION; top-grade glossy paper PWRA4-20 manufactured by KODAK JAPANLTD.; and the like.

A water-based ink related to the present teaching will be explained. Thewater-based ink related to the present teaching contains a colorant andwater.

The colorant contains a self-dispersible pigment of which mean particlediameter (average particle size) is not less than 130 nm, and aresin-dispersed pigment. Here, the “mean particle diameter (averageparticle size)” means an average particle size of secondary particlesrather than primary particles. The “secondary particle” means a particlewhich is formed by an aggregation of the primary particles. This is alsoapplicable to those described later on.

The self-dispersible pigment is dispersible in water without using anydispersing agent, for example, owing to the fact that at least one ofthe hydrophilic functional group and the salt thereof including, forexample, a carbonyl group, a hydroxyl group, a carboxylic acid group, asulfonic group, and a phosphate group is introduced into the surfaces ofthe particles of the pigment by the chemical bond directly or with anygroup intervening therebetween. By using a self-dispersible pigmentmodified by a phosphate group, it is possible to obtain a particularlyhigh optical density (OD value). As the self-dispersible pigment, it ispossible to use a self-dispersible pigment in which the pigment issubjected to a treatment by any one of methods described, for example,in Japanese Patent Application Laid-open No. 8-3498 corresponding toU.S. Pat. No. 5,609,671, Published Japanese Translation of PCTInternational Publication for Patent Application No. 2000-513396corresponding to U.S. Pat. No. 5,837,045, Published Japanese Translationof PCT International Publication for Patent Application No. 2008-524400corresponding to United States Patent Application Publications No. US2006/0201380, Published Japanese Translation of PCT InternationalPublication for Patent Application No. 2009-515007 corresponding toUnited States Patent Application Publication No. US 2007/0100023 andUnited States Patent Application Publications No. US 2007/0100024,Published Japanese Translation of PCT International Publication forPatent Application No. 2011-515535 corresponding to United States PatentApplication Publications No. US 2009/0229489, etc. It is possible touse, as a material for the self-dispersible pigment, for example, carbonblack, an inorganic pigment, an organic pigment, etc. The carbon blackis exemplified, for example, by furnace black, lamp black, acetyleneblack, channel black, etc. The inorganic pigment is exemplified, forexample, by titanium oxide, inorganic pigments based on iron oxide,inorganic pigments based on carbon black, etc. The organic pigment isexemplified, for example, by azo-pigments such as azo lake, insolubleazo-pigment, condensed azo-pigment, chelate azo-pigment, etc.;polycyclic pigments such as phthalocyanine pigment, perylene and perynonpigments, anthraquinone pigment, quinacridone pigment, dioxadinepigment, thioindigo pigment, isoindolinone pigment, quinophthalonepigment etc.; dye lake pigments such as basic dye type lake pigment,acid dye type lake pigment etc.; nitro pigments; nitroso pigments;aniline black daylight fluorescent pigment; and the like. As pigmentsdifferent from the above-described pigments are exemplified, forexample, by C. I. Pigment Blacks 1, 6, and 7; C. I. Pigment Yellows 1,2, 3, 12, 13, 14, 15, 16, 17, 55, 74, 78, 150, 151, 154, 180, 185, and194; C. I. Pigment Oranges 31 and 43; C. I. Pigment Reds 2, 3, 5, 6, 7,12, 15, 16, 48, 48:1, 53:1, 57, 57:1, 112, 122, 123, 139, 144, 146, 149,166, 168, 175, 176, 177, 178, 184, 185, 190, 202, 221, 222, 224, and238; C. I. Pigment Violet 19, 196; C. I. Pigment Blues 1, 2, 3, 15,15:1, 15:2, 15:3, 15:4, 16, 22, and 60; C. I. Pigment Greens 7 and 36;and the like. The carbon black, which is suitable to have the surfacetreatment performed therefor, includes, for example, carbon blacks suchas “MA8”, “MA100” and “#2650” produced by MITSUBISHI CHEMICALCORPORATION, etc.

As the self-dispersible pigment, it is allowable to use, for example,any commercially available product. The commercially available productincludes, for example, “CAB-O-JET (trade name) 200”, “CAB-O-JET (tradename) 250C”, “CAB-O-JET (trade name) 260M”, “CAB-O-JET (trade name)270Y”, “CAB-O-JET (trade name) 300”, “CAB-O-JET (trade name) 400”,“CAB-O-JET (trade name) 450C”, “CAB-O-JET (trade name) 465M” and“CAB-O-JET (trade name) 470Y” produced by CABOT CORPORATION; “BONJET(trade name) BLACK CW-2”, and “BONJET (trade name) BLACK CW-3” producedby ORIENT CHEMICAL INDUSTRIES, LTD.; and “LIOJET (trade name) WD BLACK002C” produced by TOYO INK MFG. CO., LTD. It is allowable that only onekind of the self-dispersible pigment as described above is used singly,or two or more kinds of the self-dispersible pigment are used incombination.

As described above, the mean particle diameter (average particle size)of the self-dispersible pigment is not less than 130 nm. The meanparticle diameter of the self-dispersible pigment may be, for example,in a range of 130 nm to 200 nm, in a range of 130 nm to 170 nm, or in arange of 150 nm to 170 nm. The mean particle diameter can be calculated,for example, by performing dilution such that the solid content amountis 0.02% by weight and by performing measurement using a dynamic lightscattering particle diameter distribution measuring apparatus “LB-550”manufactured by HORIBA, LTD., with the intensity of scattered light asthe reference for the mean particle diameter. This is also applicable tothose described later on.

The resin-dispersed pigment (resin-dispersible pigment, resin dispersiontype pigment) is dispersible in water by, for example, apigment-dispersing resin (resin dispersant). A pigment which may be usedas the resin-dispersed pigment is not particularly limited, and isexemplified, for example, by the above-described pigments which areusable as the material for the self-dispersible pigment such as carbonblack, an inorganic pigment, an organic pigment, etc. The carbon blackis exemplified, for example, by furnace black, lamp black, acetyleneblack, channel black, etc. The inorganic pigment is exemplified, forexample, by inorganic pigments based on carbon black, etc. The organicpigment is exemplified, for example, by aniline black daylightfluorescent pigment, etc. Further, any pigments different from thoselisted above can be used, provided that such pigments are dispersible inaqueous phase. Specific examples of the pigment include, for example, C.I. Pigment Blacks 1, 6, and 7, etc. As the resin dispersant, it isallowable to use a general resin dispersant. The resin-dispersed pigmentmay be encapsulated by the resin dispersant. It is allowable that onlyone kind of the resin-dispersed pigment as described above is usedsingly, or two or more kinds of the resin-dispersed pigment are used incombination.

As described above, it is allowable to use, as a the pigment-dispersingresin or the resin for dispersing pigment (resin dispersant), anypigment-dispersing resin of a general type, such as those exemplifiedby: proteins such as gelatin, albumin, casein, etc.; natural rubberssuch as gum arabic, gum traganth, etc.; glucosides such as saponin,etc.; naturally-occurring polymers such as lignin sulfonate, shellac,etc.; anionic polymers such as acrylic acid-acrylic acid ester copolymerand salt thereof, polyacrylate, polymethacrylate, salt ofstyrene-acrylic acid copolymer, salt of vinylnaphthalene-acrylic acidcopolymer, salt of styrene-maleic acid copolymer, salt of maleicacid-maleic anhydride copolymer, salt of vinylnaphthalene-maleic acidcopolymer, sodium salt of β-naphthalenesulfonic acid formalincondensate, orthophosphate, etc.; nonionic polymers such as polyvinylalcohol, polyvinyl pyrrolidone, etc.; and the like.

The blending amount of the pigment-dispersing resin (resin dispersant)with respect to the entire amount of the water-based ink is notparticularly limited, and can be determined appropriately in accordancewith the kind of the resin-dispersed pigment, the pigment solid contentamount of the pigment, etc. The ratio of the solid content weight of theresin dispersant with respect to the pigment solid content weight of theresin-dispersed pigment in the water-based ink is, for example, in arange of 0.10 to 0.60 or in a range of 0.15 to 0.50.

The mean particle diameter (average particle size) of theself-dispersible pigment is in a range of 1.5 times to 3 times the meanparticle diameter (average particle size) of the resin-dispersedpigment. The mean particle diameter of the self-dispersible pigment maybe, for example, in a range of 1.5 times to 2 times, in a range of 1.5times to 1.8 times, or in a range of 1.5 times to 1.7 times the meanparticle diameter of the resin-dispersed pigment. Further, thedifference between the mean particle diameter of the self-dispersiblepigment and the mean particle diameter of the resin-dispersed pigmentis, for example, not less than 50 nm, in a range of 50 nm to 100 nm, orin a range of 50 nm to 80 nm. The mean particle diameter of theresin-dispersed pigment is, for example, is in a range of 50 nm to 130nm, in a range of 70 nm to 110 nm, or in a range of 80 nm to 100 nm.

As described above, according to the present teaching, by using theself-dispersible pigment of which mean particle diameter is not lessthan 130 nm and the resin-dispersed pigment in combination, and makingthe mean particle diameter of the self-dispersible pigment to be in arange of 1.5 times to 3 times the mean particle diameter of theresin-dispersed pigment, it is possible to realize both the high opticaldensity (OD value) in a case of performing recording on the plain paper,and the high fixing property to the glossy paper. The mechanism for thisis presumed, for example, as follows. Namely, in the plain paper, theresin-dispersed pigment also remains on a surface of the plain paperowing to the filling effect by the self-dispersible pigment having thelarge mean particle diameter, thereby making it possible to obtain ahigh optical density (OD value). In the glossy paper, concavities andconvexities (unevenness, irregularity) generated on a surface of theglossy paper by the self-dispersible pigment having the large meanparticle diameter are leveled by the resin-dispersed pigment having thesmall mean particle diameter, and further the resin-dispersed pigment iswrapped (enveloped) by the resin dispersant, thereby enhancing thefixing property. This mechanism, however, is merely a presumption, andthe present teaching is not limited to or restricted by this presumedmechanism.

A ratio (S:R) of a solid content weight (S) of the self-dispersiblepigment to a solid content weight (R) of the resin-dispersed pigment inthe water-based ink is, for example, in a range of S:R=6:4 to 9:1, orS:R=7:3 to 8:2. In a case that the ratio (S:R) is in the range of 7:3 to8:2, it is possible to obtain a water-based ink which is more excellentin the balance between the optical density (OD value) when performingrecording on the plain paper and the fixing property to the glossypaper. The solid content weight (R) is a weight only of the pigment, anddoes not include the weight of the resin dispersant. The solid contentweight (S) is, for example, in a range of 2.4% by weight to 8.1% byweight, in a range of 3.0% by weight to 7.2% by weight, or in a range of3.5% by weight to 6.4% by weight. The solid content weight (R) is, forexample, in a range of 0.4% by weight to 3.6% by weight, in a range of0.5% by weight to 3.2% by weight, or in a range of 1.0% by weight to2.4% by weight.

A sum (S+R) of the solid content weight (S) and the solid content weight(R) is, for example, in a range of 4% by weight to 9% by weight or in arange of 5% by weight to 8% by weight.

The water-based ink may be an achromatic color ink having an achromaticcolor such as the black color, etc., or may be a chromatic color inkhaving a chromatic color (color ink). Since the achromatic color inksuch as black color ink, etc., is required to have a high opticaldensity (OD value), the achromatic color ink is suitable for thewater-based ink related to the present teaching. For example, it isallowable that each of the self-dispersible pigment and theresin-dispersed pigment may be carbon black. It is allowable that theself-dispersible pigment and the resin-dispersed pigment may be pigmentsof a same kind, or may be pigments of different kinds. Further, it isallowable that the self-dispersible pigment and the resin-dispersedpigment may be pigments of a same color, or may be pigments of differentcolors.

The water is preferably ion-exchange water or purified water (purewater). The blending amount of the water with respect to the entireamount of the water-based ink may be, for example, a balance of theother components.

The water-based ink may further contain a water-soluble organic solvent.The water-soluble organic solvent is exemplified, for example, by ahumectant which prevents the water-based ink from drying at an end of anozzle in an ink-jet head, a penetrant which adjusts the drying velocityon a recording medium, etc.

The humectant is not particularly limited, and is exemplified, forexample, by lower alcohols such as methyl alcohol, ethyl alcohol,n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,and tert-butyl alcohol; amides such as dimethylformamide anddimethylacetamide; ketones such as acetone; ketoalcohols (ketonealcohols) such as diacetone alcohol; ethers such as tetrahydrofuran anddioxane; polyethers such as polyalkylene glycol; polyvalent alcoholssuch as alkylene glycol, glycerol, trimethylolpropane,trimethylolethane, etc.; 2-pyrrolidone; N-methyl-2-pyrrolidone;1,3-dimethyl-2-imidazolidinone; and the like. The polyalkylene glycol isexemplified, for example, by polyethylene glycol, polypropylene glycol,etc. The alkylene glycol is exemplified, for example, by ethyleneglycol, propylene glycol, butylene glycol, diethylene glycol,triethylene glycol, dipropylene glycol, tripropylene glycol,thiodiglycol, hexylene glycol, etc. It is allowable that only one kindof the humectant as described above is used singly, or two or more kindsof the humectant are used in combination. Among the above-describedhumectants, the humectant is preferably a polyvalent alcohol such asalkylene glycol, glycerol, etc.

The blending amount of the humectant in the entire amount of thewater-based ink is, for example, in a range of 0% by weight to 95% byweight, in a range of 5% by weight to 80% by weight, or in a range of 5%by weight to 50% by weight.

The penetrant is not particularly limited, and is exemplified, forexample, by glycol ether. The glycol ether is not particularly limited,and is exemplified, for example, by ethylene glycol methyl ether,ethylene glycol ethyl ether, ethylene glycol-n-propyl ether, diethyleneglycol methyl ether, diethylene glycol ethyl ether, diethyleneglycol-n-propyl ether, diethylene glycol-n-butyl ether, diethyleneglycol-n-hexyl ether, triethylene glycol methyl ether, triethyleneglycol ethyl ether, triethylene glycol-n-propyl ether, triethyleneglycol-n-butyl ether, propylene glycol methyl ether, propylene glycolethyl ether, propylene glycol-n-propyl ether, propylene glycol-n-butylether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether,dipropylene glycol-n-propyl ether, dipropylene glycol-n-butyl ether,tripropylene glycol methyl ether, tripropylene glycol ethyl ether,tripropylene glycol-n-propyl ether, tripropylene glycol-n-butyl ether,etc. One kind of the penetrant may be used singly, or two or more kindsof the penetrant may be used in combination.

The blending amount of the penetrant in the entire amount of thewater-based ink may be, for example, in a range of 0% by weight to 20%by weight, in a range of 0% by weight to 15% by weight, or in a range of1% by weight to 10% by weight.

In a case that the glycol ether is used as the penetrant, and in a casethat the blending amount of the glycol ether is too large, there is sucha fear that the glycol ether might dissolve the dispersant of theresin-dispersed pigment and might lower the fixing property to theglossy paper.

The water-based ink may further contain an anionic surfactant. Theanionic surfactant is exemplified, for example, by alkyl sulfate salt,alkyl sulfate ester salt, alkyl ether sulfate ester salt, alkylbenzenesulfonate, alkyl phosphate, α-olefin sulfonate sodium salt (sodiumα-olefin sulfonate), sulfosuccinate, etc. As the anionic surfactant, forexample, a commercially available product may be used. The commerciallyavailable product is exemplified, for example, by anionic surfactantsproduced by LION SPECIALTY CHEMICALS CO., LTD., including “LIPOLAN(trade name)” series, “LIPON (trade name)” series, “SUNNOL (trade name)”series, “LIPOTAC (trade name) series, ENAGICOL (trade name)” series,“LIPAL (trade name)” series, and “LOTAT (trade name)” series, etc.;anionic surfactants produced by KAO CORPORATION including “EMAL (tradename)” series, “LATEMUL (trade name)” series, “VENOL (trade name)”series, “NEOPELEX (trade name)” series, NS SOAP, KS SOAP, OS SOAP, and“PELEX (trade name)” series, etc.; anionic surfactants produced by SANYOCHEMICAL INDUSTRIES, LTD. including “SANDET (trade name)” series and“BEAULIGHT (trade name)” series, etc.; anionic surfactants produced byTOHO CHEMICAL INDUSTRY CO., LTD. including “ALSCOPE (trade name)”series, “NEOSCOPE (trade name)” series, “PHOSFANOL (trade name)” series,etc.; sodium hexadecyl sulfate, sodium stearyl sulfate, etc. produced byTOKYO CHEMICAL INDUSTRY CO., LTD.; and the like.

The blending amount of the anionic surfactant in the entire amount ofthe water-based ink is, for example, not more than 5% by weight, notmore than 3% by weight, or in a range of 0.1% by weight to 2% by weight.

The water-based ink may further contain a nonionic surfactant. As thenonionic surfactant, it is allowable to use, for example, a commerciallyavailable product. The commercial available product is exemplified, forexample, by “OLFIN (trade name) E1010”, “OLFIN (trade name) E1004”,etc., produced by NISSHIN KAGAKU KOGYO KK, etc.

The blending amount of the nonionic surfactant in the entire amount ofthe water-based ink is, for example, not more than 5% by weight, notmore than 3% by weight, or in a range of 0.1% by weight to 2% by weight.

The water-based ink may further contain a resin, in addition to theresin dispersant, for the purpose of improving the fixing propertythereof.

The water-based ink may further contain a conventionally known additive,as necessary. The additive is exemplified, for example, by pH-adjustingagents, viscosity-adjusting agents, surface tension-adjusting agents,fungicides, etc. The viscosity-adjusting agents are exemplified, forexample, by polyvinyl alcohol, cellulose, etc.

The water-based ink can be prepared, for example, by uniformly mixingthe self-dispersible pigment, the resin-dispersed pigment, water, and anoptionally other additive(s) as necessary, by a known method, and thenremoving any non-dissolved matter, etc., with a filter, etc.

The surface tension of the water-based ink is, for example, not lessthan 30 mN/m. By making the surface tension of the water-based ink to benot less than 30 mN/m, it is possible to suppress any excessivepenetration of the water-based ink into the plain paper, thereby makingit possible to obtain a higher optical density (OD value) whenperforming recording on the plain paper. The surface tension of thewater-based ink is, for example, not more than 35 mN/m. By making thesurface tension of the water-based ink to be not more than 35 mN/m, thespreading of the water-based ink on the glossy paper is promoted, andthus the fixing property to the glossy paper becomes higher. The surfacetension is a value, for example, measured at 25° C.

As explained above, according to the present teaching, by using theself-dispersible pigment of which mean particle diameter is not lessthan 130 nm and the resin-dispersed pigment in combination, and makingthe mean particle diameter of the self-dispersible pigment to be in arange of 1.5 times to 3 times the mean particle diameter of theresin-dispersed pigment, it is possible to realize both the high opticaldensity (OD value) in a case of performing recording on the plain paper,and the high fixing property to the glossy paper.

Next, an ink cartridge (an example of an ink container) of the presentteaching will be explained. The ink cartridge of the present teaching ischaracterized by being an ink cartridge containing a water-based ink forink-jet recording; wherein the water-based ink is the water-based inkfor ink-jet recording of the present teaching as described above.Namely, the ink cartridge (ink container) related to the presentteaching contains the water-based ink for ink-jet recording of theabove-described present teaching in the inside thereof. Any known mainbody (body) of an ink cartridge can be used as the main body of the inkcartridge of the present teaching.

Next, explanation will be given about an ink-jet recording apparatusrelated to the present teaching.

The ink-jet recording apparatus related to the present teaching is anink-jet recording apparatus characterized by including: an inkaccommodating section configured to accommodate an ink therein; and anink discharge mechanism configured to discharge the ink accommodated inthe ink accommodating section; wherein the ink accommodated in the inkaccommodating section is the water-based ink related to the presentteaching.

The FIGURE depicts the configuration of an example of the ink-jetrecording apparatus related to the present teaching. As depicted in theFIGURE, an ink-jet recording apparatus 1 related to the present teachingincludes four ink cartridges (ink containers) 2, an ink dischargemechanism (ink-jet head) 3, a head unit 4, a carriage 5, a driving unit6, a platen roller 7 and a purge device 8 as main constitutivecomponents or parts.

The four ink cartridges 2 contain water-based inks of four colors,respectively, the four colors being yellow, magenta, cyan and black. Forexample, the water-based black ink is the water-based ink for ink-jetrecording related to the present teaching. In this example, a set of thefour ink cartridges 2 is described. However, it is allowable to use anintegrated ink cartridge of which interior (inner part) is partitionedso as to form an accommodating section for the water-based yellow ink,an accommodating section for the water-based magenta ink, anaccommodating section for the water-based cyan ink and an accommodatingsection for the water-based black ink, instead of using the set of thefour ink cartridges 2. As the body of the ink cartridge, it is possibleto use, for example, a publicly known body.

The ink-jet head 3 disposed on the head unit 4 performs recording on arecording medium P (for example, recording paper or recording sheet Psuch as plain paper, glossy paper, etc.). The four ink cartridges 2 andthe head unit 4 are provided or arranged on the carriage 5. The drivingunit 6 reciprocates the carriage 5 in a linear direction. As the drivingunit 6, it is possible to use, for example, a known driving unit (see,for example, Japanese Patent Application laid-open No. 2008-246821corresponding to United States Patent Application Publication No.US2008/0241398). The platen roller 7 extends in the reciprocatingdirection of the carriage 5 and is arranged to face or be opposite tothe ink-jet head 3.

The purge device 8 sucks or draws unsatisfactory ink (poor ink) whichcontains air bubbles, etc. accumulated or trapped in the inside of theink-jet head 3. As the purge device 8, it is possible to use, forexample, a known purge device (see, for example, Japanese PatentApplication laid-open No. 2008-246821 corresponding to United StatesPatent Application Publication No. US2008/0241398).

A wiper member 20 is provided on the purge device 8, at a position onthe side of the platen roller 7 such that the wiper member 20 isadjacent to the purge device 8. The wiper member 20 is formed to have aspatula shape, and wipes a nozzle-formed surface of the ink-jet head 3accompanying with the movement (reciprocating movement) of the carriage5. In the FIGURE, a cap 18 is provided to cover a plurality of nozzlesof the ink-jet head 3 which is returned to a reset position uponcompletion of the recording, so as to prevent the water-based inks fromdrying.

In the ink-jet recording apparatus 1 of the present embodiment, the fourink cartridges 2 are provided, together with the head unit 4, on onecarriage 5. However, the present teaching is not limited to this. In theink-jet recording apparatus 1, the respective four ink cartridges 2 maybe provided on a carriage which is different (separate) from thecarriage on which the head unit 4 is provided. Alternatively, therespective four ink cartridges 2 may be arranged and fixed inside theink-jet recording apparatus 1, rather than being provided on thecarriage 5. In such aspects, for example, each of the four inkcartridges 2 and the head unit 4 which is provided on the carriage 5 areconnected with a tube, etc., and the water-based inks are supplied fromthe four cartridges 2, respectively, to the head unit 4 via the tubes.Further, in these aspects, it is allowable to use, as the inkcontainers, four ink bottles having a bottle shape, instead of using thefour ink cartridges 2. In such a case, each of the ink bottles may beprovided with an inlet port via which the ink is poured from the outsideto the inside of the ink bottle.

Ink-jet recording using the ink-jet recording apparatus 1 is performed,for example, in the following manner. Namely, at first, a recordingpaper P is supplied or fed, for example, from a paper feeding cassetteor sheet feeding cassette (not depicted in the drawing) arranged at aside of or at a position below the ink-jet recording apparatus 1. Therecording paper P is introduced or guided between the ink-jet head 3 andthe platen roller 7. Then, a predetermined recording is performed on thefed or introduced recording paper P with the water-based ink(s)discharged or jetted from the ink-jet head 3. The recording paper Pafter the recording is discharged from the ink-jet recording apparatus1. According to the present teaching, it is possible to obtain arecorded matter having a high optical density (OD value) in a case ofperforming recording on the plain paper, and to obtain a recorded matterexcellent in the fixing property in a case of performing recording onthe glossy paper. In the FIGURE, the paper feeding mechanism and paperdischarge mechanism for the recording paper P are omitted in thedrawing.

In the apparatus depicted in the FIGURE, an ink-jet head of serial type(serial type ink-jet head) is adopted. However, the present teaching isnot limited to this. The ink-jet recording apparatus may be an apparatusadopting an ink-jet head of line type (line type ink-jet head).

The ink-jet recording method of the present teaching is an ink-jetrecording method characterized by including: performing recording on arecording medium by discharging, to the recording medium, a water-basedink by an ink-jet system; and using the water-based ink for ink-jetrecording related to the present teaching, as the water-based ink. Therecording includes printing a letter (text), printing an image,printing, etc.

EXAMPLES

Next, examples related to the present teaching will be explainedtogether with comparative examples. Note that the present teaching isnot limited to and is not restricted by the examples and the comparativeexamples which will be described below.

<Preparation of Aqueous Pigment Dispersions 1 and 2>

40 g of Carbon Black “#2650” produced by MITSUBISHI CHEMICAL CORPORATIONwas mixed with 200 g of ion-exchanged water, followed by beingpulverized by a bead mill. The pulverized mixture was added with acarboxyl group agent, followed by being heated and agitated, andsubjected to an oxidation processing. The obtained liquid was cleanedwith a solvent for several times, was poured into water, and was cleanedagain with the water in a repeated manner. Then, the liquid wasfiltrated with a filter, and thus a water (aqueous) pigment dispersion 1indicated in TABLE 1 was obtained. Further, a water pigment dispersion 2as indicated in TABLE 1 was obtained in a similar manner regarding theaqueous pigment dispersion 1 except for appropriately changing thecomponent rate and the duration time of dispersing process. The meanparticle diameters (sizes) of the carbon blacks contained in the aqueouspigment dispersions 1 and 2, respectively, were measured by using thedynamic light scattering particle diameter distribution measuringapparatus “LB-550” (product name) manufactured by HORIBA, LTD., and themean particle diameters were 150 nm and 120 nm, respectively.

<Preparation of Aqueous Pigment Dispersions 3 and 4>

Aqueous pigment dispersions 3 and 4 in each of which a pigment wasdispersed in water by a dispersant were prepared by the followingmethod. Pure water (purified water) was added to 20% by weight of apigment (carbon black of which mean particle diameter was 95 nm) and 7%by weight of a styrene-acrylic acid copolymer neutralized by sodiumhydroxide (acid value: 175 mgKOH/g, molecular weight: 10000) so that theentire amount thereof was 100% by weight, followed by being agitated andmixed, and thus a mixture was obtained. The obtained mixture was placedin a wet sand mill charged with zirconia beads of which diameter was 0.3mm, and was subjected to a dispersing process for 6 hours. Afterwards,the zirconia beads were removed by a separator, and the mixture wasfiltrated through a cellulose acetate filter (pore size 3.00 μm). Thus,an aqueous pigment dispersion 3 indicated in TABLE 1 was obtained. Notethat the styrene-acrylic acid copolymer is a water-soluble polymer whichis generally used as a dispersant for pigment (pigment dispersant).Further, an aqueous pigment dispersion 4 indicated in TABLE 1 wasobtained in a similar manner regarding the aqueous pigment dispersion 3except for appropriately changing the kind of pigment (mean particlediameter), the component rate and the duration time of dispersingprocess.

Examples 1 to 11 and Comparative Examples 1 to 9

Components, except for the aqueous pigment dispersions 1 to 4, whichwere included in Water-based Ink Composition (TABLE 1) were mixeduniformly or homogeneously; and thus an ink solvent was obtained.Subsequently, the ink solvent was added to each of the aqueous pigmentdispersions 1 to 4, followed by being mixed uniformly, and thus amixture was obtained. After that, the obtained mixture was filtratedthrough a cellulose acetate membrane filter (pore size 3.00 μm) producedby TOYO ROSHI KAISHA, LTD., and thus a water-based ink for ink jetrecording of each of Examples 1 to 11 and Comparative Examples 1 to 9indicated in TABLE 1 were obtained. Note that in TABLE 1, the ratiobetween the mean particle diameters indicates as to the mean particlediameter of the self-dispersible pigment is which times the meanparticle diameter of the resin-dispersed pigment; the surface tension ofthe water-based ink is a value which was measured at 25° C. by using asurface tensiometer model name: CBVP-Z manufactured by KYOWA INTERFACESCIENCE CO., LTD.

With respect to the water-based inks of Examples 1 to 11 and ComparativeExamples 1 to 9, respectively, (a) Evaluation of the optical density (ODvalue) in plain paper and (b) Evaluation of the fixing property toglossy paper were performed by the following methods.

(a) Evaluation of the Optical Density (OD Value) in Plain Paper

An ink-jet printer “MFC-J4510” manufactured by BROTHER KOGYO KABUSHIKIKAISHA was used to record an image on a plain paper (“Office Paper”manufactured by FUJITSU LIMITED) by using each of the water-based inksof Examples 1 to 11 and Comparative Examples 1 to 9. Thus, evaluationsamples were produced. The optical density (OD value) was measured atthree locations (portions) in each of the evaluation samples by using aspectrophotometric colorimetry meter “SpectroEye” (light source: D₅₀;field: 2°; density reference: ANSI-T) manufactured by X-RITE INC., andan average value of the optical density in the three locations wasobtained. Further, the optical density (OD value) in the plain paper wasevaluated according to the following evaluation criterion.

<Criterion for Evaluation of Optical Density (OD Value) in Plain Paper>

A: The optical density (OD value) was not less than 1.09.

B: The optical density (OD value) was in a range of not less than 1.02to less than 1.09.

C: The optical density (OD value) was less than 1.02.

(b) Evaluation of the Fixing Property to Glossy Paper

The ink-jet printer “MFC-J4510” was used to record an image on a glossypaper (“BP71G” manufactured by BROTHER KOGYO KABUSHIKI KAISHA) by usingeach of the water-based inks of Examples 1 to 11 and ComparativeExamples 1 to 9. Thus, evaluation samples were produced. The evaluationsamples were used to evaluate the fixing property to the glossy paperaccording to the following evaluation criterion.

<Criterion for Evaluation of Fixing Property to Glossy Paper>

AA: Any dirtied portion (smudge) was not generated in a case that theevaluation sample was rubbed after 3 minutes since the recording.

A: Although a dirtied portion (smudge) was generated in a case that theevaluation sample was rubbed after 3 minutes since the recording, anydirtied portion (smudge) was not generated in a case that the evaluationsample was rubbed after 10 minutes since the recording.

B: Although a dirtied portion (smudge) was generated in a case that theevaluation sample was rubbed after 10 minutes since the recording, anydirtied portion (smudge) was not generated in a case that the evaluationsample was rubbed after 1 hour since the recording.

C: A dirtied portion (smudge) was generated in a case that theevaluation sample was rubbed even after 1 hour since the recording.

The water-based ink composition and the results of evaluations of eachof the water-based inks of Examples 1 to 11 and Comparative Examples 1to 9 are indicated in TABLE 1.

TABLE 1 EXAMPLES 1 2 3 4 5 6 Water- Aqueous pigment dispersion 1 (S)(*1) 4 3.5 3.5 4 4 4.5 based Aqueous pigment dispersion 2 (S) (*2) — — —— — — Ink Aqueous pigment dispersion 3 (R) (*3) 1 1.5 1.5 1 1 0.5Composition Aqueous pigment dispersion 4 (R) (*4) — — — — — — (% byJONCRYL (trade name) 60 (*5) — — 0.3 — — — weight) JONCRYL (trade name)537 (*6) — — — — — — Glycerol 28  28   26   — 26  28   Triethyleneglycol — — — 30  — — Triethylene glycol-n-butyl ether 5 5   5   5 5 5  OLFIN (trade name) E1010 (*7)   0.3 0.3 0.3   0.3 — 0.3 OLFIN (tradename) E1004 (*8) — — — —   0.1 — Water balance balance balance balancebalance balance S:R 8:2 7:3 7:3 8:2 8:2 9:1 Ratio between mean particlediameters (x times)   1.6 1.6 1.6   1.6   1.6 1.6 Surface tension (mN/m)33  33   33   33  31  33   Evaluation of optical density (OD value) inplain paper A A A A A A Evaluation of fixing property with respect toglossy paper A A A A A B EXAMPLES 7 8 9 10 11 Water- Aqueous pigmentdispersion 1 (S) (*1) 3 4 4 4 6 based Aqueous pigment dispersion 2 (S)(*2) — — — — — Ink Aqueous pigment dispersion 3 (R) (*3) 2 1 1 1 2Composition Aqueous pigment dispersion 4 (R) (*4) — — — — — (% byJONCRYL (trade name) 60 (*5) — — — — — weight) JONCRYL (trade name) 537(*6) — — — — — Glycerol 28  26  26  26  22  Triethylene glycol — — — — —Triethylene glycol-n-butyl ether 5 5 5 5 5 OLFIN (trade name) E1010 (*7)  0.3 1 — —   0.3 OLFIN (trade name) E1004 (*8) — —   0.3 — — Waterbalance balance balance balance balance S:R 6:4 8:2 8:2 8:2 7.5:2.5Ratio between mean particle diameters (x times)   1.6   1.6   1.6   1.6  1.6 Surface tension (mN/m) 33  29  29  36  33  Evaluation of opticaldensity (OD value) in plain paper B B B A A Evaluation of fixingproperty with respect to glossy paper A A A B A COMPARATIVE EXAMPLES 1 23 4 5 6 7 8 9 Water- Aqueous pigment dispersion 1 (S) (*1) 5 5 5 5 8 8 —— 3.5 based Aqueous pigment dispersion 2 (S) (*2) — — — — — — — 3.5 —Ink Aqueous pigment dispersion 3 (R) (*3) — — — — — — 5 1.5 —Composition Aqueous pigment dispersion 4 (R) (*4) — — — — — — — — 1.5 (%by JONCRYL (trade name) 60 (*5) —   0.3 —   1.0   1.0   3.0 — — —weight) JONCRYL (trade name) 537 (*6) — —   0.3 — — — — — — Glycerol 27 27  27  21  21  18  28  28   28   Triethylene glycol — — — — — — — — —Triethylene glycol-n-butyl ether 5 5 5 5 5 5 5 5   5   OLFIN (tradename) E1010 (*7)   0.3   0.3   0.3   0.3   0.3   0.3   0.3 0.3 0.3 OLFIN(trade name) E1004 (*8) — — — — — — — — — Water balance balance balancebalance balance balance balance balance balance S:R — — — — — — — 7:37:3 Ratio between mean particle diameters (x times) — — — — — — — 1.31.2 Surface tension (mN/m) 33  33  33  33  33  33  33  33   33  Evaluation of optical density (OD value) in plain paper A A A C Not NotC C A Evaluation of fixing property with respect to glossy paper C C C Bavailable available AA B C TABLE 1 (following) - LEGEND (*1): Aqueousdispersion of self-dispersible carbon black; mean particle diameter: 150nm; numeral in the table indicates pigment solid content weight. (*2):Aqueous dispersion of self-dispersible carbon black; mean particlediameter: 120 nm; numeral in the table indicates pigment solid contentweight. (*3): Aqueous dispersion of carbon black (containing resindispersant); mean particle diameter: 95 nm; numeral in the tableindicates pigment solid content weight. (*4): Aqueous dispersion ofcarbon black (containing resin dispersant); mean particle diameter: 130nm; numeral in the table indicates pigment solid content weight. (*5):Resin solution; manufactured by BASF SE (former JOHNSON POLYMER CO.,LTD.); numeral in the table indicates solid content weight. (*6): Resinsolution; manufactured by BASF SE (former JOHNSON POLYMER CO., LTD.);numeral in the table indicates solid content weight. (*7): Surfactant,manufactured by NISSHIN KAGAKU KOGYO KK; numeral in the table indicateseffective ingredient amount. (*8): Surfactant, manufactured by NISSHINKAGAKU KOGYO KK; numeral in the table indicates effective ingredientcontent amount.

As indicated in TABLE 1, in Examples 1 to 11, the result of evaluationof optical density (OD value) in the plain paper and the result ofevaluation of fixing property to the glossy paper were satisfactory. Inparticular, Examples 1 and 2, each satisfying S:R=7:3 to 8:2, were moreexcellent in the balance between the optical density (OD value) in theplain paper and the fixing property to the glossy paper, than Examples 6and 7 each having a similar condition (composition) to that of Examples1 and 2 except for the S:R being S:R=9:1 and S:R=6:4, respectively.Further, Example 5 having the surface tension of 31 mN/m was moreexcellent in the optical density (OD value) in the plain paper thanExamples 8 and 9 each having the surface tension of 29 mN/m due to thechange in the blending amount of the surfactant added thereto; andExample 5 having the surface tension of 31 mN/m was more excellent inthe fixing property to the glossy paper than in Example 10 having thesurface tension of 36 mN/m due to the change in the blending amount ofthe surfactant added thereto.

On the other hand, in Comparative Examples 1 to 3 each not using theresin-dispersed pigment, the result of evaluation of the fixing propertyto the glossy paper was unsatisfactory. In Comparative Examples 4 to 6each not using the resin-dispersed pigment, the blending amount of theresin (JONCRYL (trade name)) was increased for the purposed of improvingthe fixing property to the glossy paper, than those in ComparativeExamples 1 to 3. However, in Comparative Example 4, the result ofevaluation of the optical density (OD value) in the plain paper wasunsatisfactory; in Comparative Examples 5 and 6, the evaluations couldnot be performed due to the increased viscosity and aggregation.Further, in Comparative Example 7 not using the self-dispersiblepigment, the result of evaluation of the optical density (OD value) inthe plain paper was unsatisfactory. Furthermore, in Comparative Example8 in which the mean particle diameter of the self-dispersible pigmentwas less than 130 nm, the result of evaluation of the optical density(OD value) in the plain paper was unsatisfactory. Moreover, inComparative Example 9 in which the mean particle diameter of theself-dispersible pigment was less than 1.5 times the mean particlediameter of the resin-dispersed pigment, the result of evaluation of thefixing property to the glossy paper was unsatisfactory.

As described above, the water-based ink related to the present teachingis capable of realizing both the high optical density (OD value) in thecase of performing recording on the plain paper, and the high fixingproperty to the glossy paper. The applicability of the water-based inkrelated to the present teaching is not particularly limited, and iswidely applicable to a variety of kinds of ink-jet recording.

What is claimed is:
 1. A water-based ink for ink-jet recordingcomprising: water; a resin-dispersed pigment; and a self-dispersiblepigment of which mean particle diameter is not less than 130 nm, and isin a range of 1.5 times to 3 times mean particle diameter of theresin-dispersed pigment.
 2. The water-based ink for ink-jet recordingaccording to claim 1, wherein a ratio (S:R) of a solid content weight(S) of the self-dispersible pigment to a solid content weight (R) of theresin-dispersed pigment in the water-based ink is in a range of 6:4 to9:1.
 3. The water-based ink for ink-jet recording according to claim 1,wherein a ratio (S:R) of a solid content weight (S) of theself-dispersible pigment to a solid content weight (R) of theresin-dispersed pigment in the water-based ink is in a range of 7:3 to8:2.
 4. The water-based ink for ink-jet recording according to claim 1,wherein a sum (S+R) of a solid content weight (S) of theself-dispersible pigment and a solid content weight (R) of theresin-dispersed pigment in the water-based ink is in a range of 4% byweight to 9% by weight.
 5. The water-based ink for ink-jet recordingaccording to claim 1, wherein surface tension of the water-based ink isnot less than 30 mN/m.
 6. The water-based ink for ink-jet recordingaccording to claim 1, wherein surface tension of the water-based ink isnot more than 35 mN/m.
 7. The water-based ink for ink-jet recordingaccording to claim 1, wherein difference between the mean particlediameter of the self-dispersible pigment and the mean particle diameterof the resin-dispersed pigment is not less than 50 nm.
 8. Thewater-based ink for ink-jet recording according to claim 1, wherein eachof the self-dispersible pigment and the resin-dispersed pigment iscarbon black.
 9. The water-based ink for ink-jet recording according toclaim 1, further comprising triethylene glycol-n-butyl ether.
 10. Thewater-based ink for ink-jet recording according to claim 1, wherein themean particle diameter of the self-dispersible pigment is in a range of1.5 times to 2 times the mean particle diameter of the resin-dispersedpigment.
 11. The water-based ink for ink-jet recording according toclaim 1, wherein the mean particle diameter of the self-dispersiblepigment is in a range of 1.5 times to 1.7 times the mean particlediameter of the resin-dispersed pigment.
 12. The water-based ink forink-jet recording according to claim 1, wherein the mean particlediameter of the self-dispersible pigment is in a range of 130 nm to 200nm.
 13. The water-based ink for ink-jet recording according to claim 1,wherein the mean particle diameter of the self-dispersible pigment is ina range of 150 nm to 170 nm.
 14. The water-based ink for ink-jetrecording according to claim 1, wherein the mean particle diameter ofthe self-dispersible pigment is in a range of 150 nm to 170 nm, and isin a range of 1.5 times to 1.7 times the mean particle diameter of theresin-dispersed pigment.
 15. An ink container which accommodates thewater-based ink for ink-jet recording as defined in claim 1.